jspi cleanup: remove the asyncify-era residue — dead code, conditionals, pipeline scaffolding, stale prose

The runtime is JSPI-only; this removes everything that still pretended
otherwise. Three exhaustive sweeps (C++/JS+build+CI/tests+docs) drove
the inventory; every deletion verified by grep closure + full gates.

Broken-right-now fixes:
- deploy-staging.yml passed the retired opt_level input — the workflow
  could not even start. Removed.
- env.sh carried dead exports with a live -sASYNCIFY=1 inside
  (WASM_LDFLAGS/PTHREAD_LDFLAGS, zero consumers). Removed; the
  WASM_LEGACY_EXCEPTIONS rationale rewritten to the real reason.
- docker/build.sh exported PCBJAM_ASYNC_BACKEND (read nowhere). Gone.

Dead weight removed:
- binaryen submodule (nothing builds or invokes it), wasm-opt-bench
  workflow + scripts/bench/, get-wasm-opt.sh, diagnostics.js (242 lines
  of Asyncify-API-only code), the KICAD_PIPELINE background-postprocess
  scaffolding (existed to parallelize the deleted wasm-opt phase; the
  postprocess is a seconds-long node script and now runs inline),
  build-monitor's dead asyncify rows, sched-context orphan build
  output, dead .gitignore entries, the .jspi-assets spike dir (the two
  wf-result research JSONs moved to docs/features/async/migration-evidence/).
- bindings: fiber_park.h + its 12 embind registrations (broken-if-
  called under JSPI), the kicadOpenFileStart/OPEN_JOB starter route,
  main_stack_runner.h + 5 includes, the always-null context-sleep weak
  hook in nanosleep_yield.c.
- shim: the backend field (installed-flag idempotency instead),
  noteContextWait (dead both sides), the __wxAsyncifyDump alias (+ the
  WasmTool fallback and string-dump normalize branch).
- web: the emscripten-6-ignored mainScriptUrlOrBlob option in boot.ts
  (gerber-demo keeps it: it loads the deployed CDN release, which
  predates emscripten 6 — noted inline).

Conditionals: all 'backend === jspi' checks reduced to scheduler-
presence checks; races_quiescent re-keyed from Asyncify.state (vacuous)
to real backlog quiescence (resumeReady/mutatorQueue — NOT _windowLive,
which is the probing activation's own window by definition).

Renames (identifiers only, no file renames): ASYNC_LINK_FLAGS→
JSPI_LINK_FLAGS and Makefile ASYNC_LDFLAGS→JSPI_LDFLAGS,
kicadCollabFiberBusy→kicadCollabBusy (embind + web + tests),
collab_common.h fiber*→apply*/coroutine naming, asyncifySignatures→
wasmTrapSignatures (lists byte-identical).

Tests: the two remaining vacuous [wx-asyncify]/fiber-resume-refused
asserts re-keyed to live JSPI beacons; eeschema-load's failure message
no longer sends the developer to a deleted script; wait-beacons' dead
families/parser deleted; lane-0 legacy-glue guards removed (lane 0 is
unconstructible); the embind test.fail re-gated with the JSPI reason
(plain embind invokers cannot suspend — verified still failing);
lint-determinism now scans tests/jspi (166 files clean);
eeschema-collab local-move gated to chromium (~50% flaky on FF even
solo; pcbnew twin covers both engines).

Docs: DEBUG.md rewritten as the JSPI debugging guide; build.md
describes the single-phase build; docs/features/async/README.md
banner-marked historical and repointed at the NEW
23-jspi-runtime.md (current architecture: export census, turnstile,
libcontext ownership + refusal contract, embind call shapes, the
em-pthread service-wrapper trick, exception policy, known gaps).

Gates on the cleaned tree: test:e2e 725 passed / 0 failed (after the
quiescence-probe fix; the 3 other reds were verified contention flakes
solo-green or the documented FF gate), web 76/0, jspi 18/18 both
engines, vitest 295/295 + 17/17, all lints green, live-app census
clean.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_016X9eh1s5sTx1o9Em9KBuwR

scripts/build-monitor.sh

@@ -91,6 +91,7 @@ BEGIN {
     # Canonical per-app stage rows, in order. Sub-stages (wxwidgets-configure /
     # -compile) fold into the wxwidgets row via parent[].
     ROWN = 0
+    ord[++ROWN] = "container-sync";  lab["container-sync"]  = "Sync source to container"
     ord[++ROWN] = "deps";            lab["deps"]            = "Dependencies"
     ord[++ROWN] = "wxwidgets";       lab["wxwidgets"]       = "wxWidgets"
     ord[++ROWN] = "kicad-stubs";     lab["kicad-stubs"]     = "Stub libraries"
@@ -98,10 +99,7 @@ BEGIN {
     ord[++ROWN] = "kicad-compile";   lab["kicad-compile"]   = "KiCad compile"
     ord[++ROWN] = "kicad-bitmaps";   lab["kicad-bitmaps"]   = "Bitmap resources"
     ord[++ROWN] = "copy-output";     lab["copy-output"]     = "Copy output"
-    ord[++ROWN] = "binaryen";        lab["binaryen"]        = "Build Binaryen"
-    ord[++ROWN] = "dyncall-shims";   lab["dyncall-shims"]   = "dynCall shims"
-    ord[++ROWN] = "finalize";        lab["finalize"]        = "Finalize WASM"
-    ord[++ROWN] = "asyncify";        lab["asyncify"]        = "Asyncify"
+    ord[++ROWN] = "env-shim";        lab["env-shim"]        = "ENV merge shim"
     for (i = 1; i <= ROWN; i++) ridx[ord[i]] = i
     parent["wxwidgets-configure"] = "wxwidgets"
     parent["wxwidgets-compile"]   = "wxwidgets"
@@ -152,12 +150,11 @@ curRawKey == "kicad-compile" {
     if ($0 ~ /Configuring KiCad with CMake/)      h_phase = "kicad-configure"
     if ($0 ~ /\(CMake target:/)                   h_phase = "kicad-compile"
     if ($0 ~ /Building bitmap resources/)         h_phase = "kicad-bitmaps"
-    if ($0 ~ /Applying asyncify transformation/)  h_phase = "asyncify"
     if (h_phase == "kicad-compile" && match($0, /[0-9]+%\]/)) {
         p = substr($0, RSTART, RLENGTH); gsub(/[^0-9]/, "", p); h_pct = p + 0
     }
     if (h_phase == "kicad-compile" && $0 ~ /Building (C|CXX) object/) h_cc++
-    if ($0 ~ /Build complete\. Output files/ || $0 ~ /Asyncify complete/) h_done = 1
+    if ($0 ~ /Build complete\. Output files/) h_done = 1
 }
 END {
     if (markerCount > 0) { render_markers(); }
@@ -173,8 +170,6 @@ function render_markers(   state, totalEl, pk, curIdx, i, k, st, det, subdet, en
         printf "H|-|0|0|%d|%s\n", totalEl, state
         if (curRawKey == "container-sync") {
             printf "R|active|Sync source to container|%s\n", fmt(termTs - rowStartTs["container-sync"])
-        } else if (curRawKey == "binaryen") {
-            printf "R|active|Build Binaryen|%s\n", fmt(termTs - rowStartTs["binaryen"])
         } else {
             printf "N|waiting for build to start...\n"
         }
@@ -234,13 +229,12 @@ function render_heuristic(   state, order, ph, i, k, st, names) {
     }
     printf "N|(no progress markers in this log - inferred from log text)\n"
     # Reduced ordered phase set we can detect heuristically.
-    split("wxwidgets kicad-configure kicad-compile kicad-bitmaps asyncify", order, " ")
+    split("wxwidgets kicad-configure kicad-compile kicad-bitmaps", order, " ")
     names["wxwidgets"]="wxWidgets"; names["kicad-configure"]="KiCad configure (CMake)"
     names["kicad-compile"]="KiCad compile"; names["kicad-bitmaps"]="Bitmap resources"
-    names["asyncify"]="Asyncify"
     ph = 0
-    for (i = 1; i <= 5; i++) if (order[i] == h_phase) ph = i
-    for (i = 1; i <= 5; i++) {
+    for (i = 1; i <= 4; i++) if (order[i] == h_phase) ph = i
+    for (i = 1; i <= 4; i++) {
         k = order[i]
         if (h_done) st = "done"
         else if (i < ph) st = "done"